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SCAPE+

Introduction

Predecessor version

SCAPE (Soft Cliff And Platform Erosion) is a modelling tool that can be applied to cliff/platform coasts, with (or without) a beach. It represents processes, but does so in abstract and behavioural terms and is typically used to simulate change over timeframes of decades to centuries. It is also used to model the short-term rapid responses of cliffs to the removal of coast protection.

SCAPE was developed by Mike Walkden and Jim Hall at the University of Bristol between 1999 and 2002, and was first described in Walkden & Hall (2005). It is a quasi 3D model (Q3D) in that the coast is described as a series of shore-normal profiles, which interact through the exchange of sediment. Although its original purpose was to model the recession of coastal cliffs, it actually represents the shaping of shore platforms (the cliff essentially retreats with the upper limit of the platform). From the outset it was intended that relatively long periods of time would be represented, and that engineering interventions would be accounted for. It was also designed so that run times would be sufficiently short to allow the exploration of uncertainty through the application of probabilistic techniques.

A non-traditional approach was adopted to achieve these objectives. Model development was informed by a Systems perspective of costal geomorphology. From this perspective the cliff/ platform profile was assumed to emerge from the interactions of a set of elements including the cliff, shore platform and beach, in response to marine forcing at various scales. Order arises from these interactions due to feedback; generally speaking negative feedback allows the emergence of dynamic stability.

This approach proved quite fruitful. SCAPE has been successfully applied to deal with practical coastal management problems and has also yielded new insights into the fundamental behaviour of this type of coast, particularly in response to climate change.

The first site to be modelled with SCAPE was the Naze peninsula in Essex (Walkden & Hall, 2005). Although those simulations were undertaken within a research project they were successfully used to represent the consequences of alternative coastal management options over a 50 year timeframe.

Following this success, SCAPE was used (in 2002) to represent the coast of North Norfolk (later published by Walkden & Hall, 2011) as part of a formal Coastal Strategy Study on behalf of North Norfolk District Council. In order to capture the large spatial scale, elements of the code were simplified, including the representation of the effect of groynes to produce a Regional version of the original Quasi-3D model (SCAPE Q3DR). Key strengths of that study were the representation of a long stretch of coast (35 km), successfully capturing the long and complex historic record of shore recession, simulation of the alongshore effects of coast protection structures and exploration of alternative scenarios of coastal management and future sea level rise.

The regional Norfolk model was subsequently developed with funding from the Tyndall Centre for Climate Change Research and adopted as a geomorphological engine in its Regional Coastal Simulator (see Dickson et al., 2007, Dawson et al, 2009, Walkden et al., 2009, and Nicholls et al., 2015). That funding allowed the Norfolk model to be extended (to 50km), coupled with a model of (coastal) flooding of the Norfolk Broads (see Dawson et al., 2009), and applied in a strongly probabilistic manner. This model was subsequently used in a second Coastal Strategy Study for North Norfolk District Council, in 2012/13.

SCAPE was also used within the Defra/EA funded Management of Cohesive Foreshores project. This involved modelling Warden Point (on the Isle of Sheppy) and (though unsuccessfully) Easington on the Holderness coast.

The Tyndall Centre and the Environment Agency also funded research that used SCAPE to explore the basic relationship between sea level rise and shore recession rate. In a large set of 2D simulations, the sensitivity to increased sea level rise was explored as certain parameters were varied (including tidal range, wave height and rock strength). A simple relationship was found, and this was expressed in an equation intended to be simple to apply in coastal management projects (Walkden & Dickson, 2008, Ashton et al., 2011). This equation and a SCAPE model were used to predict the long term erosion of the region of coast fronting Accra, Ghana (Appeaning-Addo et al., 2008).

In 2008/9 SCAPE was used within the project Characterisation and prediction of large scale, long-term change of coastal geomorphological behaviours in a proof of concept to explore the coupled behaviour of an (hypothetical) open coast and an estuary; the latter being represented by an ASMITA model (Walkden & Rossington, 2009).

SCAPE has also been coupled to TELEMAC (Chini et al., 2010) and used to represent sites (inspired by locations on the Isle of Wight) with across-shore variations in geology (Carpenter et al., 2014).

In recent years applications have been largely commercial, and have included new models of the shores of Drigg (Cumbria), West Somerset, and the Wash. SCAPE simulations have also been used to inform work on coastal catch-up in the Clacton area and at Happisburgh.

The Environment Agency-funded project Cliff and Shore Sensitivity to Accelerated Sea Level Rise has extended the earlier work into the generic response of cliff/platform shores to accelerated relative sea level rise and to the removal of coast protection structures (Walkden et al., 2015). That project included models of the shores of Holderness (though unsuccessfully) Nash Point (Glamorgan) Birling Gap (Sussex), Happisburgh (Norfolk) and Drigg (Cumbria).

Further details of SCAPE+, including its conceptualisations and structure can be found in the User Guide, and in the various publications referred to above (and listed in the References Tab).

Conceptual developments under iCOASST

iCOASST has supported the development of the regional SCAPE code (Q3DR) into SCAPE+. The new code has been rationalised and extended to include new processes and greater detail. It has also been made Open and OpenMI compatible.

The rationalisation process has included the extraction of embedded parameters into a setup file, to make SCAPE+ models more readily adaptable and various assumptions more explicit. An important part of the rationalisation of the code was the removal of routines that were either experimental, strongly site specific, or too time consuming to make appropriately robust.

Key developments are:

Compliance with OpenMI standards

In technical terms, the OpenMI (Open Modelling Interface) Standard is a software component interface definition. In practical terms, it is one approach to tackling the problem of how to link numerical models so that they may interact as they run. SCAPE+ is OpenMI compliant and, so can exchange sediment at its boundaries, with other OpenMI compliant models.

Variation in geological strength

Geological strength has been made fully variable, both alongshore and in the vertical domain. This has been implemented to provide the user with the capability to represent variations in geology both along and across the shore.

Van Rijn model representation

The code has been developed to allow the user to use the van Rijn (2015) formula for longshore transport. This was included to give more flexibility to the user in the representation of beach transport, particularly for locations of larger grain size. The CERC equation may also be used.

RegFalls3

RegFalls3 is a statistical model of cliff stability developed by Jim Hall, and described in Dawson et al, 2009. It has been used in the past to convert SCAPE predictions of cliff toe position into cliff top retreat. Previously this was done in an offline or ad-hock manner; RegFalls3 has now been embedded within SCAPE+.

Vellinga beach profiles

The SCAPE+ code can now be used to represent beach profiles defined using the 'Vellinga' approach. This alternative to the Bruun profile has been introduced as a means of estimating a more dynamic beach surface level, to support prediction of (for example) seawall stability, wave impact loading and wave overtopping.

Wave celerity look-up tables

SCAPE+ now accepts user-defined look-up tables for wave celerity and wave group celerity. In the past these were pre-defined, which limited the range of wave conditions that could be represented. Default look-up tables may still be used in SCAPE+, but the user also has the flexibility to define new tables to represent more extreme conditions.

Timestamped relative sea levels

The timeframes around the response of consolidated shore profiles to changes in rates of sea level rise are long. Relative sea level changes should not, therefore, be treated as a stationary driver of profile change as, for example, wave climate might be. For this reason the sea level input to SCAPE+ has been timestamped, to encourage the user to recognise and account for medium to long term changes in rate of sea level rise/fall.

Variation in tidal range

SCAPE+ has been developed to represent variations in tidal range along the coast; this brings potential advantages in areas such as Suffolk (UK) where alongshore gradients in tidal level can be large. Development of a vertical grid to support the simulation of coastal barriers A vertical grid has been developed and coupled to the original horizontal SCAPE grid. The intention is that this will support the subsequent development of modules of horizontal features landward of the shoreline.

Development of a vertical grid to support the simulation of coastal barriers

A vertical grid has been developed and coupled to the original horizontal SCAPE grid. The intention is that this will support the subsequent development of modules of horizontal features landward of the shoreline.

Other developments have been made to support the application of SCAPE+ to practical problems, including allowing:
  • more extensive control of the model and its output via the setup file;
  • both high and low resolution output;
  • limiting of transport conditions at the model boundaries;
  • High angle waves to be excluded;
  • Input of matrices to describe groyne efficiency and conditions of cross shore transport during storms.

In addition the model now has an optional spin-up period, and may be run in a start or restart mode and the range and adaptability of output files has been extended.

Use in iCOASST

The two main uses made of SCAPE+ in the iCOASST project were to explore the behaviour of linked cliff and barrier coasts and to build elements of the Deben model 'composition' (the Suffolk case study). In other work SCAPE+ was also used to explore the modes of development of low-lying shores (inundation, erosion and accretion) over long periods of time.

Behaviour of linked cliff-barrier coasts

These simulations tackled the problem of modelling the decadal to (multiple) century scale evolution of coupled cliff/ barrier coasts in Suffolk, UK. A study site (the Suffolk coast between Southwold and Kessingland) was first interpreted, taking the approach of coupling geomorphic assessment with Causal Loop Analysis. This approach was taken to both understand and represent key feedback pathways governing the response of such shores. Initial modelling with the SCAPE+ tool (with a simplistic treatment of the barrier profile) showed broad scale cliff/ barrier interaction, and self-regulation of shoreline shape. Initial simulations of the response of the system to accelerated sea level rise were also run.

This work is described in Walkden, M., Payo, A, Barnes, J., and Burningham, H, 2015. Modeling the response of coupled barrier and cliff systems to sea level rise. In Proceedings of Coastal Sediments, San Diego.

The Deben composition

SCAPE+ was also used to model the sections of coast flanking the inlet of the River Deben. These extended (on the Felixstowe side) to Cobbalds Point and (on the Bawdsey side) beyond Shingle street. These models were linked (within a FluidEarth, OpenMI composition) via a MESOi model of the Deben inlet features. The composition was driven by inshore wave conditions derived (via a transfer function approach) from TOMOWAC simulations.

The inlet features included a set of interacting shoals (some attached to the shore) that exchanged material in response to supply and demand from the neighbouring coasts, and also through internal diffusion. Material moving south along the Bawdsey frontage tended to move into the inlet shoals, and circulate within them. This circulation could be characterised by the periodic break-down of the largest of the shoals, and the subsequent movement of the released material to the (Felixstowe) shoreline. Some material was exported to continue south along the Felixstowe frontage.

The dynamics of the composition were also linked to the development of the Deben estuary, via its tidal prism. The equilibrium volumes of the inlet shoals varied with the prism, and this affected both its ability to store material and therefore the periodicity of shoal break-down. The (long term) timeseries of the Deben tidal prism was derived using elements of an ESTEEM model. Coastal management was represented via the construction/ removal of coast protection at Bawdsey and Shingle Street, and also by the removal of sea defences within the estuary.

The composition, was used to explore a set of scenarios of future change, involving increased sea level rise, changed wave height and direction, and alternative management of the coast and estuary. Both the composition and the simulations are described in more detail here

Evaluation for end-users

As part of the Environment Agency project "Embedding iCOASST into practice", HR Wallingford have undertaken an independent evaluation of the usability of the iCOASST models. Each of the models have been downloaded from this website, compiled and run using (i) the documentation and (ii) the site-specific data sets on which they have been developed (also provided on this website). The outcome of this evaluation for this model can be found here and should be referenced by anyone interested in using or developing the model further.